In the paper industry, and more particularly in the field of paper-based containers for foodstuff, such as milk carton, ice cream carton, soft drink or coffee cups to name a few, the containers are usually made from paper-based substrates coated on both surfaces with polyethylene coatings. Such polyethylene coatings allow the protection of the interior of the container, which is in contact with the foodstuff, and also the exterior of the container. For instance, polyethylene coatings on the exterior surface of the container provide protection against water condensation thereby limiting or avoiding deterioration of the carton when the foodstuff in the container is colder than ambient temperature. Polyethylene coatings on the interior surface of the container may provide protection against water and/or moisture and/or oil and/or grease. Foamed polyethylene coatings may also provide other features to the container such as heat transfer prevention when the foodstuff in the container is a hot foodstuff such as coffee for instance.
Polyethylene coatings are generally applied by extrusion onto the paper-based substrate. In some cases, a primer coating can be applied to the substrate before extrusion of the polyethylene to enhance adhesion thereof.
When erecting the container, a portion of the paper surface, which will face the interior of the container and be in contact with the goods therein (e.g. foodstuff), covers a portion of the other surface, which will form the exterior of the container, and the superimposed portions are “glued” together using heat and/or pressure. Good adhesion between the two coatings, through sealing, is required to maintain integrity of the container in use. Good sealing (through heat-sealing) is usually observed when the coatings are of the same nature on both surfaces of the paper-based substrate, such as for polyethylene coatings.
However, extruded polyethylene coatings commonly used in the field, are difficult to recycle and/or generally not repulpable and/or non-compostable and/or non-biodegradable, which makes them less environmental friendly.
Moreover, polyethylene coatings need to be corona treated to increase their surface tension in order to ease the printing on the surface of the coated substrate (e.g. on the exterior surface), requiring a further step in the coating process, the coating process being an in-line or an off-line process.
In view of the above, there is a need for coated paper-based substrates for manufacturing containers to hold goods such as foodstuff or any other type of goods, which would be able to overcome or at least minimize the above-discussed prior art concerns.